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The R20 battery — also referred to as the D battery, D cell, LR20, or UM1 — is a standardized large cylindrical dry-cell battery with a nominal voltage of 1.5 V. Its designation follows the IEC 60086 international standard, where "R" denotes a round (cylindrical) cell and "20" refers to the standardized size code assigned by the International Electrotechnical Commission.

In everyday language the terms R20 battery and D battery are often used interchangeably. Technically, however, "D" is the North American size label while "R20" is the IEC designation that describes the physical dimensions regardless of the internal chemistry. When the battery uses alkaline chemistry it is more precisely called LR20; the zinc-carbon variant retains the plain R20 designation.

Because of its relatively large volume, the R20 cell can pack significantly more active material than smaller formats such as AA (R6) or AAA (R03). This translates directly into higher capacity and longer runtimes — making it the preferred power source for devices that draw moderate to high currents over extended periods.

The physical dimensions and electrical characteristics of the R20 battery are governed by IEC 60086-2. The table below lists the key parameters for quick reference.

R20 batteries are available in several distinct chemical formulations. Each offers a different balance of capacity, cost, shelf life, and suitability for various drain levels. Understanding the differences helps you select the optimal cell for any application.

Zinc-Carbon (R20)

The original and most economical R20 chemistry. Zinc-carbon cells use a zinc anode and a manganese dioxide cathode separated by an ammonium chloride electrolyte paste. Capacity ranges from roughly 6,000 to 8,000 mAh, and performance degrades noticeably under heavy loads. Best suited for low-drain, intermittent-use devices such as wall clocks and TV remote controls.

Alkaline (LR20)

The most widely used R20 variant, alkaline cells employ a potassium hydroxide electrolyte that significantly improves efficiency, capacity, and performance under load compared with zinc-carbon. Capacity reaches 10,000 – 18,000 mAh and shelf life extends up to seven years. The alkaline LR20 is the go-to choice for most household and commercial applications.

Lithium Iron Disulfide (FR20)

Non-rechargeable lithium D cells deliver superior energy density and outstanding cold-weather performance — they remain effective at temperatures as low as −40 °C. Although more expensive, they are ideal for critical or high-drain applications where reliability is paramount, such as emergency lighting or professional equipment used in extreme environments.

Nickel-Metal Hydride — NiMH (HR20)

Rechargeable NiMH D cells offer a nominal voltage of 1.2 V and can be cycled hundreds of times, making them the most cost-effective and environmentally friendly option for frequently used, high-drain devices. Low-self-discharge (LSD) NiMH variants retain their charge for months in storage, making them practical for emergency kits as well.

Nickel-Cadmium — NiCd (KR20)

An older rechargeable chemistry offering robust performance and a flat discharge curve, though with lower capacity than modern NiMH cells. NiCd batteries contain cadmium, a toxic heavy metal, and should be disposed of through designated e-waste recycling channels.

The D cell (R20) sits at the top of the common cylindrical battery size range. The table below compares it with other popular consumer battery formats.

As the data makes clear, the R20 battery holds three to six times the energy of a standard AA cell at the same 1.5 V, which explains why devices requiring sustained power — such as large handheld flashlights or portable boomboxes — rely on the D-size format.

The R20 battery excels in any application that demands sustained high current output or a long continuous runtime between battery changes. Its classic use case remains the large handheld flashlight, but R20 cells appear across a surprisingly diverse range of consumer, industrial, and emergency applications.

Frequently Asked Questions